1. Field of the Invention
This invention relates generally to implantable medical devices, and more particularly to apparatus for connecting the lead or catheter to the implantable device.
2. Description of the Prior Art
At present, the most widely used implantable medical device is the cardiac pacemaker. The modern pacer system includes a pacing lead and an implantable pulse generator or pacemaker.
Pacers, which provide therapeutic stimulation to the heart to correct conduction disorders, have been a treatment of choice since the early 1960's. The earliest pacemakers included a battery-powered pulse generator which was physically connected to an integral catheter or lead system. In use, the electrodes of the lead system would be sutured directly to the myocardium of the heart while the pulse generator would be implanted subcutaneously under the skin. This early pacemaking system utilized Dow Corning Silastic rubber as the principle covering material to ensure biocompatibility, while the electronic portion of the pacer was imbedded or "potted" in Scotch Cast 5 epoxy which has been manufactured by the 3M Company. Electrode areas were typically made from stainless steel or platinum-iridium alloy.
Improvements in the delivery of pacer therapy have resulted in the modern form of pacer which includes a hermetically sealed pulse generator which is readily connected to a separate lead system.
In general, the connection between the pacer or pulse generator and the lead is made in a, so called "connector block" which is attached to body of the pacer. This connector block is typically formed from transparent plastic and it contains structures to facilitate both, electrical connection and mechanical coupling between the implanted lead system and the pacer. Feed-throughs, located in part in the connector block, provide electrical connection between the electronic components within the pacer and the connector block contacts.
In the prior art, set screws and cross-drilled contact blocks have been used to couple the lead to the feed through. This simple expedient permits good electrical and mechanical contact. However, unless certain precautions are taken, it is possible to over, or under, tighten the set screw which can lead to poor coupling. One example of a particularly successful set screw system of the type discussed above, is known from U.S. Pat. No. 4,226,244 to Coury et al.
A number of alternatives to the manually tightened set screw have been proposed. For example, U.S. Pat. No. 4,540,236 to Peers-Trevarton teaches a "push-button" style release structure; U.S. Pat. No. 4,712,557 teaches inter alia, a wedge member to lock the lead in the pacer; and, U. S. Pat. No. 4,105,037 teaches a bayonet type of attachment between the lead and the pacer.